Remove testtube import

Extractor got deleted in remitamine/youtube-dl@8af2804

youtube_dl/extractor/__init__.py

@@ -687,7 +687,6 @@ from .telemb import TeleMBIE
 from .teletask import TeleTaskIE
 from .tenplay import TenPlayIE
 from .testurl import TestURLIE
-from .testtube import TestTubeIE
 from .tf1 import TF1IE
 from .theintercept import TheInterceptIE
 from .theonion import TheOnionIE